1. Field of the Invention
The present invention relates generally to implantable blood filters. More particularly, the invention relates to caval filters having sonographically conspicuous features.
2. Related Art
Advances in many surgical specialties have saved the lives of many patients suffering serious illness or injury, and have improved the quality of life of countless others. However, such surgical repair of organs and tissues can disrupt the body's plumbing, e.g., the circulatory system, sufficiently to give rise to new risks. For this reason, minimally invasive techniques have been developed, for example wherein highly specialized surgical tools are manipulated from outside a patient's body through a catheter or tube inserted through a tiny incision or puncture and guided to a surgical site. Yet, both invasive and minimally invasive procedures disturb circulation sufficiently so that arterial plaques can become dislodged or clots can form in the bloodstream and move with the circulation with the body. Such debris, moving along with normal circulation, can become lodged in and partially or completely block vessels supplying blood and oxygen to critical organs, such as the heart, lungs and brain.
Medication is often used to reduce the likelihood of blood clot formation during and after surgery, however, post-operative thrombosis, as such blood clot formation is called, remains an important problem to be solved. Therefore, filters implantable in a patient's body using minimally invasive techniques have been developed. By appropriately positioning such filters, dangerous blood clots can be removed from circulation and held in a safe location until they can be dissolved by medication or extracted, again using minimally invasive techniques. Thus, there has been a significant reduction in the incidence of morbidity and mortality due to post-operative embolism which occurs when a thrombolus moves from its site of formation to block a vessel, becoming an embolus.
Conventional implantable blood filters employing a variety of geometries are known. Many are generally basket or cone shaped, in order to provide adequate clot-trapping area while permitting sufficient blood flow. Also known are filters formed of various loops of wire, including some designed to partially deform the vessel wall in which they are implanted.
Along with their many functional shapes, conventional filters may include other features. For example, peripheral loops or arms may be provided to perform a centering function so that a filter is accurately axially aligned with the vessel in which it is implanted. In order to prevent migration under the pressure induced by normal circulation, many filters have anchoring features. Such anchoring features may include sharp points, ridges, etc. Finally, conventional filters are known which have specific features for facilitating implanting and extracting using catheterization. Thus, a surgeon can select from a variety of conventional filters, to optimize one or another parameter of interest, and implant or extract that filter using minimally invasive techniques.
The minimally invasive techniques mentioned above require that a surgeon guide a catheter to a precise location within a patient's body. The precise location within the body is visualized using conventional x-ray imaging and marked on the patient's body with marker or using x-ray fluoroscopy during surgery. The position of the catheter or other instrument within the body is visualized using similar techniques. As is well-known, x-rays, a form of ionizing radiation, produce an image showing by variations in image density corresponding variations in transmission density indicative of the position of various anatomical structures and of the instrument introduced into the body by the surgeon. In order to improve the fluoroscopic image of soft tissues, such as blood vessels, contrast media are sometimes introduced into a vessel to be imaged. An instrument which might otherwise be radiologically transparent may also be given a radiopaque tip or other feature. However, exposure to ionizing radiation or contrast media is contraindicated for a significant number of patients, such as pregnant women or patients exhibiting anaphylactic reactions to contrast media.